Muspac and Catedral are two of the most important gas- and condensate-producing fields in southern Mexico. They produce from Cretaceous fractured carbonates. The objective of this integrated study is to define the stratigraphic and structural controls that caused early water production in those fields.
Open-hole log correlation of 45 wells served to define eight reservoir zones, based on petrophysical characteristics. Petrophysical properties were mapped using a volumetric parameter to analyze the anisotropy of the gas-storage capacity in the fields. Dipmeter and borehole image logs were interpreted in 14 wells using cumulative dip and vector plot techniques to define unconformities, flooding surfaces, and faults. Borehole images from five wells were extremely useful in detecting evidence of sedimentologic and structural features. Fracture density depends on petrophysical properties of the reservoir rocks. In-situ stress directions were determined in 18 wells using borehole breakouts to define the predominant northwest-southeast orientation of the open fractures. Two dominant fracture sets, determined from seismic attributes and borehole images, are parallel to seismically determined faults.
According to this study, early water production is caused by coning through fractures, faults, and karstic zones. Some water-producing intervals depend on the location of perforations, especially when these are located in highly fractured rocks and close to the gas-water contact. To minimize early water production, the operator must avoid wells in fault zones, wells on the flanks close to the gas-water contact, and deviated wells drilled perpendicular to the direction of open fractures.
